Organic polysulfides, especially organic trisulfides, are useful for many purposes such as additives for elastomers, antioxidants for lubricating oils, intermediates for the production of organic chemicals, insecticides, and germicides, and additives for diesel fuels to improve cetane number and ignition qualities. Organic polysulfides are also useful in the compounding of high pressure lubricants and in the acceleration of rubber treating processes.
Organic polysulfides can be produced by reacting mercaptans with elemental sulfur in the presence of a catalyst. The reaction can generally be depicted as follows: ##STR1##
where R, R.sub.1 and R.sub.2 are alkyl radicals, generally containing 1 to 20 carbon atoms, which can be the same or different, x is an integer from 2 to 1 0, and x is the average number of sulfur atoms per polysulfide molecule in the product.
The product of the above reaction typically comprises a distribution of individual organic polysulfide compositions, each containing a different number of sulfur atoms. In many commercial applications, especially for use in high pressure lubricants, organic trisulfides exhibit more desirable properties than other organic polysulfides. For example, organic polysulfides containing more than three sulfur atoms exhibit high copper-strip corrosivity (ASTM Copper Strip Corrosion Test D-130-56), rendering them unsatisfactory for many commercial applications. In addition, organic disulfides can be undesirable because they have a high flash point and exhibit poor lubrication properties.
If an organic polysulfide product contains a high quantity of organic polysulfides having more or less than three sulfur atoms, costly separation processes and equipment are necessary to remove undesirable polysulfides and recover a more pure organic trisulfide product that is suitable for commercial purposes. Therefore, a reaction product having a distribution of organic polysulfides which maximizes the amount of organic trisulfides while minimizing the amount of other organic polysulfides is desired.
Several processes exist for the preparation of high purity organic trisulfides; however, most existing processes require materials, conditions, and/or steps which make commercial implementation uneconomical. For example, the trisulfide selective process taught in U.S. Pat. No. 5,442,123 requires expensive process equipment, an expensive catalyst, and low reaction temperatures, which increase the required reaction time. Thus, it is desirable to develop a process for selectively producing organic trisulfides which minimizes equipment, labor, and time and employs a relatively inexpensive catalyst.